Fatigue experiments on hybrid welded connections made of very high strength steels

In a fatigue loaded structure made of Very High Strength Steels (VHSS) absolute and relative stress variations will be higher compared to those in structures made of lower grade steels. Stress concentrations in joints reduce the advantage of VHSS under cyclic loading. A hybrid connection, consisting of cast steel welded to a VHSS member, could make the use of VHSS relatively more efficient. If designed properly, cast steel parts could result in welded joints with low stress concentrations, by shifting welds out of the most severe stress location. In a recent test program at the Delft University of Technology hybrid VHSS plate connections have been tested under cyclic loading. In the research the yield strength of the plates has been varied. Rolled plates with grades S690 and S890 were welded to matching cast plates with grades G10MnMoV6.3 and G18NiMoCr3.6. All plates were V-welded with thickness of 25 mm. Two 4-point bending setups were used of the Stevin II Laboratory of the Faculty of Civil Engineering and Geosciences. During the fatigue tests crack growth in thickness and in width direction were measured. The fatigue strength results are presented by comparing S-N curves